Read API paths and forwarded requests as the router does

The router reads an absolute-form target's path without resolving dot
segments, so a target such as http://host/api/../x still reaches /api
middleware. Take that path the same way when deciding whether the API
response headers apply.

The Street View fallback now treats any forwarding header as forwarded, even
an empty one, before it spends the key.

src/tooling/viteBuild.test.mjs

@@ -366,6 +366,9 @@ test('every API response carries the API policy and nosniff on real dev and prev
         ['/api.x', 404],
         [`http://localhost:${port}/api/fixture/ok`, 200],
         [`http://localhost:${port}/API/nope`, 404],
+        // The router keeps dot segments in an absolute-form target's path.
+        ['http://elsewhere.example/api/../x', 404],
+        ['http://elsewhere.example/API/%2e%2e/x', 404],
         ['/api/fixture/ok', 403, policy, { host: 'elsewhere.example' }],
         // A route's own policy is added to the API policy, never replaces it.
         ['/api/fixture/own-policy', 200, `${policy}, frame-ancestors 'none'`],